Propylene polymers

ABSTRACT

The present invention relates to catalyst components for the polymerization of olefins comprising Mg, Ti, halogen and at least two electron donor compounds, said catalyst component being characterized by the fact that at least one of the electron donor compounds, present in an amount from 20 to 50% by mol with respect to the total amount of donors, is selected from esters of succinic acids which are not extractable, for more than 25% by mol and at least another electron donor compound which is extractable, for more than 35%. The said catalyst component-are capable to give polymers with high xylene insolubility, high stereoblock content and broad MWD suitable for making the polymers usable in the BOPP sector.

The present invention relates to catalyst components for thepolymerization of olefins, in particular propylene, comprising a Mgdihalide based support on which are deposited a Ti compound having atleast one Ti-halogen bond and at least two electron donor compoundsselected from specific classes. The present invention further relates tothe catalysts obtained from said components and to their use inprocesses for the polymerization of olefins. The catalysts of thepresent invention are able to give, with high yields, propylenehomopolymers characterized by high xylene insolubility, a broad range ofisotacticity and, in particular conditions by a very high content ofstereoblocks.

Catalyst components for the stereospecific polymerization of olefins arewidely known in the art. The most largely widespread family of catalystsystems comprises a solid catalyst component, constituted by a magnesiumdihalide on which are supported a titanium compound and an internalelectron donor compound, used in combination with an Al-alkyl compound.Conventionally however, when a higher crystallinity of the polymer isrequired, also an external donor (for example an alkylalkoxysilane) isneeded in order to obtain higher isotacticity. One of the preferredclasses of internal donors is constituted by the esters of phthalicacid, diisobutylphthalate being the most used. This catalyst system iscapable to give very good performances in terms of activity,isotacticity and xylene insolubility provided that an external electrondonor compound is used. When the external donor is missing, low yields,low xylene insolubility and poor isotacticity are obtained. On the otherhand, when the external donor is used, high xylene insolubility isobtained only together with a high isotacticity. Moreover, the MolecularWeight Distribution (MWD) is, under the normal single steppolymerization conditions, not broad (Polydispersity Index in the range3.6-4.5). These characteristics, although useful in certainapplications, are not desirable in certain other fields such as theproduction of bi-oriented polypropylene frlms (BOPP). For application inthis field in fact, polypropylenes are required to have a broad MWD(Polydispersity Index higher than 5) a lower flexural modulus(obtainable by lowering crystallinity of the polymer) while at the sametime retaining a high xylene insolubility. Moreover, it has been foundthat suitable polymers for application in this field are those that, inaddition to the above requirements, have also a comparatively highcontent of the so called stereoblocks, i.e., of polymer fractions which,although predominantly isotactic, contain a not negligible amount ofnon-isotatctic sequences of propylene units. In the conventionalfractionation techniques such as the TREF (Temperature Rising ElutionTemperature) those fractions are eluted at temperatures lower than thoseare necessary for the more isotactic fractions. In EP 658577 isdescribed a method for producing PP homopolymers having a highstereoblock content. It comprises polymerizing propylene in the presenceof a catalyst comprising (i) a solid catalyst component in which a Ticompound and diisobutyl phthalate are supported on a MgCl₂, (ii) anAl-alkyl compound as a co-catalyst and (iii) a3,3,3,trifluropropyl(alkyl)dimethoxysilane as external donor. In example1 it can be seen that although the polymerization is carried out in twosequential steps under different conditions, the MWD of the bimodalpolymer obtained is not sufficiently broad (Polydispersity Index 4.7).Furthermore, the bimodal polymers can have problems of homogeneity dueto presence of distinct fractions with pronounced difference in averageMw. In said example 1 the weight percentage of stereoblock fractionmeasured via TREF, on the polymer after visbrealing, is about 31%, whilein another run (in Table 2) the amount of stereoblock fraction was about26%. In view of the above, it would be desirable to have a catalystcomponent with still improved characteristics and in particular capableto give polymers with high xylene insolubility, high. stereoblockcontent and broad MWD suitable for making the polymers usable in theBOPP sector.

It has now unexpectedly been found a catalyst component having the aboveadvantages which comprises Mg, Ti, halogen and two electron donorcompounds selected from specific classes. It is therefore an object ofthe present invention a catalyst component for the polymerization ofolefins CH₂═CHR, in which R is hydrogen or a hydrocarbyl radical with1-12 carbon atoms, comprising Mg, Ti, halogen and at least two electrondonor compounds, said catalyst component being characterized by the factthat at least one of the electron donor compounds, which is present inan amount from 15 to 50% by mol with respect to the total amount ofdonors, is selected from esters of succinic acids which are notextractable, under the conditions described below, for more than 20% bymol and at least another electron donor compound which is extractable,under the same conditions, for more than 30% by mol.

According to the present invention, the esters of succinic acids notextractable for more than 20% by mol will be defined as non-extractablesuccinates. The electron donor compounds extractable for more than 30%by mol will be defined as extractable electron donor compounds.Preferably, the amount of non-extractable succinates is between 20 and45 and more preferably from 22 to 40% by mol with respect to the totalamount of the electron donor compounds. In a preferred embodiment isused a succinate which is not extractable for more than 15% and anotherelectron donor compound which is extractable for more than 35%. Amongthe non-extractable succinates mentioned above, particularly preferredare the succinates of formula (1) below

in which the radicals R₁ and R₂, equal to, or different from, each otherare a C₁-C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl,arylalkyl or alkylaryl group, optionally containing heteroatoms; and theradicals R₃ and R₄ equal to, or different from, each other, are C₁-C₂₀alkyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionallycontaining heteroatoms with the proviso that at least one of them is abranched alkyl; said compounds being, with respect to the two asymmetriccarbon atoms identified in the structure of formula (I), stereoisomersof the type (S,R) or (R,S) that are present in pure forms or inmixtures.

R₁ and R₂ are preferably C₁-C₈ alky, cycloalkyl, aryl, arylalkyl andalkylaryl groups. Particularly preferred are the compounds in which RIand R₂ are selected from primary alkyls and in particular branchedprimary alkyls. Examples of suitable R₁ and R₂ groups are methyl, ethyl,n-propyl, n-butyl, isobutyl, neopentyl, 2-ethylhexyl. Particularlypreferred are ethyl, isobutyl, and neopentyl.

Particularly preferred are the compounds in which the R₃ and/or R₄radicals are secondary alkyls like isopropyl, sec-butyl, 2-pentyl,3-pentyl or cycloakyls like cyclohexyl, cyclopentyl, cyclohexylmethyl.

Examples of the above-mentioned compounds are the (S,R) (SR) forms pureor m mixture, optionally in racemic form, of diethyl2,3-bis(trimethylsilyl)succinate, diethyl2,3-bis(2-ethylbutyl)succinate, diethyl 2,3dibenzylsuccinate, diethyl2,3-diisopropylsuccinate, diisobutyl 2,3-diisopropylsuccinate, diethyl2,3-bis(cyclohexylmethyl)succinate, diethyl 2,3-diisobutylsuccinate,diethyl 2,3-dineopentylsuccinate, diethyl 2,3-dicyclopentylsuccinate,diethyl 2,3-dicyclohexylsuccinate.

Among the extractable electron donor compounds particularly preferredare the esters of mono or dicarboxylic organic acids such as benzoates,malonates, phthalates and succinates. Among malonates particularlypreferred are those of formula (II):

where R₁ is H or a C₁-C₂₀ linear or branched alkyl, alkenyl, cycloalkyl,aryl, arylalkyl or alkylaryl group, R₂ is a C₁-C₂₀ linear or branchedalkyl, alkenyl, cycloalkyl, aryl, arylallyl or alkylaryl group, R₃ andR₄, equal to, or different from, each other, are C₁-C₂₀ linear orbranched alkyl groups or C₃-C₂₀ cycloalkyl groups.

Preferably, R₃ and R₄ are primary, linear or branched C₁-C₂₀ alkylgroups, more preferably they are primary branched C₄-C₂₀ alkyl groupssuch as isobutyl or neopentyl groups.

R₂ is preferably, in particular when R₁ is H, a linear or branchedC₃-C₂₀ alkyl, cycloalkyl, or arylalkyl group; more preferably R₂ is aC₃-C₂₀ secondary alkyl, cycloaLkyl, or arylalkyl group. Preferred estersof aromatic carboxylic acids are selected from C₁-C₂₀ alkyl or arylesters of benzoic and phthalic acids, possibly substituted. The alkylesters of the said acids being preferred. Particularly preferred are theC₁-C₆ linear or branched alkyl esters. Specific examples areethylbenzoate, n-butylbenzoate, p-methoxy ethylbenzoate, p-ethoxyethylbenzoate, isobutylbenzoate, ethyl p-toluate, diethyl phthalate,di-n-propyl phthalate, di-n-butyl phthalate, di-n-pentyl phthalate,di-i-pentyl phthalate, bis(2-ethylhexyl) phthalate, ethyl-isobutylphthalate, ethyl-n-butyl phthalate, di-n-hexyl phthalate,di-isobutylphthalate.

Among succinates there are many subclasses of compounds that can be usedas extractable donors according to the present invention. One of thepreferred groups of compounds is that described by the formula (III)

in which R₃ to R₅ are hydrogen and R₆ is a branched alkyl, cyloalkyl,aryl, arylalkyl and alkylaryl radical having from 3 to 10 carbon atoms.Particularly preferred are the compounds in which R₆ is a branchedprimary alkyl group or a cycloalkyl group having from 3 to 10 carbonatoms. Specific examples are diethyl sec-butylsuccinate, diethylthexylsuccinate, diethyl cyclopropyluccinate, diethyl norbomylsuccinate,diethyl (10)perhydronaphthylsuccinate, diethyl trimethylsilylsuccinate,diethyl methoxysuccinate, diethyl p-methoxyphenylsuccinate, diethylp-chlorophenylsuccinate diethyl phenylsuccinate, diethylcyclohexylsuccinate, diethyl benzylsuccinate, diethyl(cyclohexylmethyl)succinate, diethyl t-butylsuccinate, diethylisobutylsuccinate, diethyl isopropylsuccinate, diethylneopentylsuccinate,

Another subclass of preferred compounds is that of formula (M) in whichR₃ and R₄ are hydrogen and R₅ and R₆ are selected from C₁-C₂₀ linear orbranched alkyl, alkenyl cycloalkyl, aryl, arylalkyl or aLkylatyl group,optionally containing heteroatoms. Specific examples of suitable2,2-disubstituted succinates are: diethyl 2,2-dimethylsuccinate, diethyl2-ethyl-2-methylsuccinate, diethyl 2-benzyl-2-isopropylsuccinate,diethyl 2-(cyclohexylmethyl)-2-isobutylsuccinate, diethyl2-cyclopentyl-2-n-propylsuccinate, diethyl 2,2-diisobutylsuccinate,diethyl 2-cyclohexyl-2-ethylsuccinate, diethyl2-isopropyl-2-methylsuccinate, diethyl 2,2-diisopropyl diethyl2-isobutyl-2-ethylsuccinate, diethyl 2-(1,1,-trifluoro-2-propyl)-2-methylsuccinate, diethyl2-isopentyl-2-isobutylsuccinate, diethyl 2-phenyl-2-n-butylsuccinate,diisobutyl 2,2imethylsuccinate, diisobutyl 2-ethyl-2-methylsuccinate,diisobutyl 2-benzyl-2-isopropylsuccinate, diisobutyl2-(cyclohexylmethyl)-2-isobutylsuccinate, diisobutyl2-cyclopentyl-2-n-propylsuccinate.

Moreover, also preferred are the (S,S), (R,R) or meso forms of thesuccinates of formula (I) described above.

Mixtures of different succinates of formula (I) can be used asnon-extractable donors, and mixtures of extractable donors can be usedas well. In particular, we found it particularly advantageous the use ofthe succinates of formula (I) in which R₃ and R₄ are identical both asextractable and non extractable electron donors. Actually, the compoundsof formula (I) in which R₃ and R₄ are the same are often mixtures ofmeso (S,S and R,R) and rac- form (SR and R,S) as a direct result oftheir preparation process. Therefore, in certain cases the skilled inthe art is already provided with a mixture of extractable andnon-extractable donors to be used in the preparation of the catalyst ofthe invention. Depending on the peculiar amounts of the single donors inthe mixtures, additional amounts of extractable donors could berequested in order to bring the final composition of the catalyst withinthe limits set forth above .

It has been found particularly interesting the use of a catalystcomponent comprising the rac-form of diethyl or diisobutyl2,3-diisopropylsuccinate as non-extractable donor and the meso form ofdiethyl or diisobutyl 2,3-diisopropylsuccinate together wvith analkylphthalate as extractable donors.

As explained above, the catalyst components of the invention comprise,in addition to the above electron donors, Ti, Mg and halogen. Inparticular, the catalyst components comprise a titanium compound, havingat least a Ti-halogen bond and the above mentioned electron donorcompounds supported on a Mg halide. The magnesium halide is preferablyMgCl₂ in active form which is widely known from the patent literature asa support for Ziegler-Natta catalysts. Patents U.S. Pat. No. 4,298,718and U.S. Pat. No. 4,495,338 were the first to describe the use of thesecompounds in Ziegler-Natta catalysis. It is known from these patentsthat the magnesium dihalides in active form used as support orco-support in components of catalysts for the polymerization of olefinsare characterized by X-ray spectra in which the most intense diffractionline that appears in the spectrum of the non-active halide is diminishedin intensity and is replaced by a halo whose maximum intensity isdisplaced towards lower angles relative to that of the more intenseline. The preferred titanium compounds used in the catalyst component ofthe present invention are TiCl₄ and TiCI₃; firthermore, alsoTi-haloalcoholates of formula Ti(OR)_(n-y)X_(y) can be used, where n isthe valence of titanium, y is a number between 1 and n−1 X is halogenand R is a hydrocarbon radical having from 1 to 10 carbon atoms.

The preparation of the solid catalyst component can be carried outaccording to several methods. According to one of these methods, themagnesium dichloride in an anhydrous state, the titanium compound andthe electron donor compounds are milled together under conditions inwhich activation of the magnesium dichloride occurs. The so obtainedproduct can be treated one or more times with an excess of TiCl₄ at atemperature between 80 and 135° C. This treatment is followed bywashings with hydrocarbon solvents until chloride ions disappeared.According to a further method, the product obtained by co-milling themagnesium chloride in an anhydrous state, the titanium compound and theelectron donor compounds are treated with halogenated hydrocarbons suchas 1,2-dichloroethane, chlorobenzene, dichloromethane etc. The treatmentis carried out for a time between 1 and 4 hours and at temperature offrom 40° C. to the boiling point of the halogenated hydrocarbon. Theproduct obtained is then generally washed with inert hydrocarbonsolvents such as hexane.

According to another method, magnesium dichloride is preactivatedaccording to well known methods and then treated with an excess of TiCl4at a temperature of about 80 to 135° C. in the presence of the electrondonor compounds. The treatment with TiCI4 is repeated and the solid iswashed with hexane in order to eliminate any non-reacted TiCl₄.

A further method comprises the reaction between magnesium alcoholates orchloroalcoholates (in particular chloroalcoholates prepared according toU.S. Pat. No. 4,220,554) and an excess of TiCl₄ in the presence of theelectron donor compounds at a temperature of about 80 to 120° C.

According to a preferred method, the solid catalyst component can beprepared by reacting a titanium compound of formula Ti(OR)_(n-y)X_(y),where n is the valence of titanium and y is a number between 1 and n,preferably TiCl₄, with a magnesium chloride deriving from an adduct offormula MgCl₂pROI where p is a number between 0.1 and 6, preferably from2 to 3.5, and R is a hydrocarbon radical having 1-18 carbon atoms. Theadduct can be suitably prepared in spherical form by mixing alcohol andmagnesium chloride in the presence of an inert hydrocarbon immisciblewith the adduct, operating under stirrng conditions at the meltingtemperature of the adduct (100-130° C.). Then, the emulsion is quicklyquenched, thereby causing the solidification of the adduct in form ofspherical particles. Examples of spherical adducts prepared according tothis procedure are descnbed in U.S. Pat. No. 4,399,054 and U.S. Pat. No.4,469,648. The so obtained adduct can be directly reacted with Ticompound or it can be previously subjected to thermal controlleddealcoholation (80-130° C.) so as to obtain an adduct in which thenumber of moles of alcohol is generally lower than 3 preferably between0.1 and 2.5. The reaction with the Ti compound can be carried out bysuspending the adduct (dealcoholated or as such) in cold TiCl₄(generally 0° C.); the mixture is heated up to 80-130° C. and kept atthis temperature for 0.5-2 hours. The treatment with TiCl₄ can becarried out one or more times. The electron donor compounds can be addedduring the treatment with TiCl₄. They can be added together in the sametreatment with TiCl₄ or separately in two or more treatments.

The preparation of catalyst components in spherical form is describedfor example in European Patent Applications EP-A-395083, EP-A-553805,EP-A-553806, EPA-601525 and WO98/44009.

The solid catalyst components obtained according to the above methodshow a surface area (by B.E.T. method) generally between 20 and 500 m²/gand preferably between 50 and 400 m²/g, and a total porosity (by B.E.T.method) higher than 0.2 cm³/g preferably between 0.2 and 0.6 cm³/g. Theporosity (Hg method) due to pores with radius up to 10000 Å generallyranges from 0.3 to 1.5 cm³/g, preferably from 0.45 to 1 cm³/g.

A further method to prepare the solid catalyst component of theinvention comprises halogenating magnesium dihydrocarbyloxide compounds,such as magnesium dialkoxide or diaryloxide, with solution of TiCl₄ inaromatic hydrocarbon (such as toluene, xylene etc.) at temperaturesbetween 80 and 130° C. The treatment with TiCl₄ in aromatic hydrocarbonsolution can be repeated one or more times, and the electron donorcompounds are added during one or more of these treatments.

In any of these preparation methods the desired electron donor compoundsand in particular those selected from esters of carboxylic acids, can beadded as such or, in an alternative way, it can be obtained iin situ byusing an appropriate precursor capable to be transformed in the desiredelectron donor compound by means, for example, of known chemicalreactions such as esterification, transesterification, etc.

Regardless to the preparation method used, the final amount of the twoor more electron donor compounds is such that the molar ratio withrespect to the MgCl₂ is from 0.01 to 1, preferably from 0.05 to 0.5.

The solid catalyst components according to the present invention areconverted into catalysts for the polymerization of olefins by reactingthem with organoaluminum compounds according to known methods.

In particular, it is an object of the present invention a catalyst forthe polymerization of olefrns CH₂═CHR, in which R is hydrogen or ahydrocarbyl radical with 1-12 carbon atoms, comprising the product ofthe reaction between:

-   -   (i) the solid catalyst component as disclosed above,    -   (ii) an organo-metal compound and    -   (iii) an external electron donor compound.

The organo-metal compound (ii) is preferably chosen among alkyl-Alcompounds and in particular among the trialkyl aluminum compounds suchas for example triethylaluminum, triisobutylaluminum,tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It isalso possible to use alkylaluminum halides, alkylaluminum hydrides oralkylaluminum sesquichlorides, such as AlEt₂Cl and Al₂Et₃Cl₃, possiblyin mixture with the above cited trialkylaluminums.

Suitable external electron-donor (iii) include silanes, ethers, esters,amines, heterocyclic compounds and ketones. A particular class ofpreferred external donor compounds is that of silanes of formula R_(a)⁵R_(b) ⁶Si(OR⁷)_(c), where a and b are integers from 0 to 2, c is aninteger from 1 to 4 and the sum (a+b+c) is 4; R⁵, R⁶, and R⁷, are alkyl,alkylen, cycloalkyl or aryl radicals with 1-18 carbon atoms optionallycontaining heteroatoms. Particularly preferred are the silicon compoundsin which a is 1, b is 1, c is 2, at least one of R⁵ and R⁶ is selectedfrom branched alkyl, cycloalkyl or aryl groups with 3-10 carbon atomsoptionally containing heteroatoms and R⁷ is a C₁-C₁₀ alkyl group, inparticular methyl. Examples of such preferred silicon compounds aremethylcyclohexyldimethoxysilane, dicyclopentyldimethoxysilane.

Although the above disclosed catalyst are able to give propylenepolymers with high xylene insolubility, high stereoblock content andbroad MWD it has been found that polymers with particularly increasedstereoblock content and broad MWD are obtainable using as externaldonors certain silanes of the above disclosed formula having arelatively low stereoregulating ability. By the term “lowstereoregulating ability” we mean silanes that under the standardpolymerization conditions described below give propylene polymers with acontent of pentads (mmmm) equal to or lower than 97%. The skilled in theart can easily deterrnine the stereoregulating ability of the relevantsilanes by performing the polymerization test under the conditionsdescribed below. In addition, the applicant found that a group ofsilanes with a low stereoregulating ability are those of the formuladisclosed above in which R⁵ is methyl, R⁶ is a C1-C15 linear alkyl andR⁷ is a linear C1-C4 alyl. Preferred examples of these silanes aren-propyl-methylimethoxysilane; n-butyl-methyl-dimethoxysilane;n-pentyl-methyl-dimethoxysilane; n-hexyl-methyldiethoxysilane;n-octyl-methyl dimethoxysilane; n-decyl-methyl-dimethoxysilane. Afurther group of silanes with low stereoregulating ability is that ofthe formula above described in which c is 3 or 4. Particularly preferredare the alkyltriallkoxysilanes and the tetraalkoxysilanes in which R⁷ isa linear C1-C8 alkyl. Another group of silanes with a lowstereoregulating ability are those of the formula disclosed above inwhich R⁵ is a trifluropropyl group, optionally subustituted, R⁶ is aC1-C6 linear alkyl or a piperidinyl group, optionally substituted, andR⁷ is a linear C1-C4 alkyl. Preferred examples of these silanes are(3,3,3-trifuoro-n-propyl)(2-ethylpiperidinyl)dinethoxysilane,methyl(3,3,3-triuoro-n-propyl)dimethoxysilane.

The electron donor compound (iii) is used in such an amount to give amolar ratio between the organoaluminum compound and said electron donorcompound (ii) of from 0.1 to 500, preferably from 1 to 300 and morepreferably from 3 to 100.

The polymerization process can be carried out according to knowntechniques for example slurry polymerization using as diluent an inerthydrocarbon solvent, or bulk polymerization using the liquid monomer(for example propylene) as a reaction medium. Moreover, it is possibleto carry out the polymerization process in gas-phase operating in one ormore fluidized or mechanically agitated bed reactors.

The polymerization is generally carried out at temperature of from 20 to120° C., preferably of from 40 to 80° C. When the polymerization iscarried out in gas-phase the operating pressure is generally between 0.5and 5 MPa, preferably between 1 and 4 MPa In the bulk polymerization theoperating pressure is generally between I and 8 MPa preferably between1.5 and 5 MPa.

As explained above, the catalysts of the invention when used in thepolymerization of propylene are able to give polymers with a range ofisotacticity (expressed in term of percentage of mmmm pentads), MWD andstereoblock content such that they are particularly suitable for use inthe BOPP field. It is particular worth noting that the high values ofP.L are obtained in a single polymerization step i.e., with asubstantially monomodal distribution which allow to avoid any problemdue to non homogeneity of the product.

Therefore, it constitutes a further object of the present invention apropylene polymer having the following characteristics:

-   -   a stereoblock content of 18% or higher measured by the TREF        method described below;    -   a Polydispersity Index of at least 5 and    -   a percentage of pentads (mmmm), measured by NMR, lower than or        equal to 97.

Preferably the stereoblock content is higher than 20 and more preferablyhigher than 22. The P.I. is preferably higher than 5.3 and thepercentage of pentads is preferably lower than 96.5 and more preferablylower than 95.5. It has moreover been found that particularlyinteresting polypropylenes are those disclosed above and furthercharacterized by a showing, at the TREF analysis, a fraction eluted at atemperature ranging from 110° and 114° C. which accounts for more than25% of the total weight of the polymer. Preferably it accounts for morethan 33%. Also preferred are the polypropylenes with a TREF profile suchthat the fraction eluted at a temperature between 1150 and 120° C.accounts for a value between 0.1 and 10%, preferably between 0.5 and 5%,of the total weight of the polymer.

Characterizations

Test for the Extractability of the Electron Donor (ED) Compounds

A. Preparation of the Solid Catalyst Component

Into a 500 ml four-necked round flask, purged with nitrogen, 250 ml ofTiCl₄ were introduced at 0° C. While stirring, 10.0 g of microspheroidalMgCl₂*2.8C₂H₅OH(prepared according to the method described in ex.2 ofU.S. Pat. No. 4,399,054 but operating at 3,000 rpm instead of 10,000)were introduced. 4.4 mMols of the selected electron donor compound werealso added. The temperature was raised to 100 ° C. and maintained atthat temperature for 120 min. Then, the stirring was discontinued, thesolid product was allowed to settle and the supernatant liquid wassiphoned off.

250 ml of fresh TiCl₄ were added. The mLcture was reacted at 120° C. for60 min under stirring and, then, the supematant liquid was siphoned off.The solid (A) was washed six times with anhydrous hexane (6×100 ml) at60 ° C., dried under vacuum and analyzed for the quantitativedetermination of Mg and electron donor compound. The type of electrondonor compound and its molar ratio with respect to Mg (ratio A) arereported in Table 1.

B. Treatment of Solid A

In a 250 ml jacketed glass reactor with mechanical stirrer andfiltration septum are introduced under nitrogen atmosphere 190 ml ofanhydrous n-hexane, 19 inMmoles of AlEt₃ and 2 gr of the catalystcomponent prepared as described in A. The mixture is heated at 60° C.for 1 hour under stirring (stirring speed at 400 rpm). After that timethe mixture is filtered, washed four times with n-hexane at 60° C. andfinally dried under vacuum for 4 hours at 30° C. The solid is thenanalyzed for the quantitative determination of Mg and electron donorcompound. The type of electron donor compound and its molar ratio withrespect to Mg (ratio B) are reported in Table 1. The extractability ofthe electron donor compound is calculated according to the followingformula: % of ED extracted=(Ratio A-Ratio B)/Ratio A

Polymer Microstructure Analysis

50 mg of each xylene insoluble fraction were dissolved in 0.5 ml ofC₂D₂Cl₄

The ¹³C NMR spectra were acquired on a Bruker DPX400 (100.61 Mhz, 90°pulse, 12s delay between pulses). About 3000 transients were stored foreach spectrum; mmmm pentad peak (21.8 ppm) was used as reference.

The microstructure analysis was carried out as described in literature(Polymer, 1984, 25, 1640, by lzoue Y. et Al. and Polymer, 1994, 35, 339,by Clzujo R et Al.).

Determination of X. I.

2.5g of polymer were dissolved in 250 ml of o-xylene under stirring at135° C. for 30 minutes, then the solution was cooled to 25° C and after30 minutes the insoluble polymer was filtered. The resulting solutionwas evaporated in nitrogen flow and the residue was dried and weighed todetermine the percentage of soluble polymer and then, by difference, theX. I. %.

TREF Method

TREF fractionation of the polymer was carried out by dissolving 1 g ofpropylene polymer in o-xylene at 135° C. and slowly cooling (20 h) to25° C. in a column loaded with glass beads. Elution with o-xylene (600mL/h) was first carried out at 25° C. for 1 h to obtain a xylene-solublefraction. The column temperature was then raised from 25 to 95° C. at arate of 0.7° C./min without elution and the temperature was held at 95°C. for 2 h before eluting at this temperature for 1 h to yield a singlefraction. Finally, elution was continued while raising the temperaturefrom 95 to 120° C. at a rate of 3° C./h, collecting individual fractionsat temperature intervals of 1° C. According to the present invention thestereoblock content is considered as the total weight of the fractions,insoluble in xylene at 25° C., that are eluted at a temperature lowerthan 100° C. based on the total weight of the polymer.

Determination of Polydispersitv Index (P.I.)

This property is strictly connected with the molecular weightdistribution of the polymer under examination. In particular it isinversely proportional to the creep resistance of the polymer in themolten state. Said resistance called modulus separation at low modulusvalue (500 Pa), was determined at a temperature of 200 IC by using aparallel plates rheometer model RMS-800 marketed by RHEOMETRICS (USA),operating at an oscillation frequency which increases from 0.1 rad/secto 100 rad/sec. From the modulus separation value, one can derive theP.I. by way of the equation:P.I.=54.6*(modulus separation)^(−1.76)in which the modulus separation is defined as:modulus separation=frequency at G′=500 Pa/frequency at G″=500 Pawherein G′ is storage modulus and G′ is the loss modulus.Standard Test of Polymerization for Evaluation of Silane StereocontrolPreparation of the Solid Catalyst Component

Into a 500 mL four-necked round flask, purged with nitrogen, 250 mL ofTiCl₄ were introduced at 0° C. While stirring, 10.0 g of microspheroidalMgCl₂*2.8C₂H₅OH prepared according to the method described in ex.2 ofU.S. Pat. No. 4,399,054 but operating at 3000 rpm instead of 10000 rpm)and 10.1 mMol of diisobutylphthalate are added. The temperature wasraised to 100° C. and maintained for 120 min. Then, the stiring wasdiscontinued, the solid product was allowed to settle and thesupernatant liquid was siphoned off. Then 250 rL of fresh TiCl₄ wereadded. The mixture was reacted at 120 C for 60 min and, then, thesupernatant liquid was siphoned off. The solid was washed six times withanhydrous hexane (6×100 mL) at 60° C. Finally, the solid was dried undervacuum. In a 4 liter autoclave, purged with nitrogen flow at 70° C. forone our, are introduced in propylene flow at 30° C. 75 mL of anhydroushexane containing 800 mg of AlEt₃, an amount of silane such as toprovide an Al/Si ratio of 20 and 10 mg of a solid catalyst componentprepared as described above. The autoclave was closed. 1.5 NL ofhydrogen were added and then, under stirring, 1.2 kg of liquid propenewere fed. Ihe temperature was raised to 70° C. in five minutes and thepolymerization was carried out at this temperature for two hours. Thenonreacted propylene was removed, the polymer was collected, dried at70° C. under vacuum for three hours, weighed, and subject. to xyleneinsolubility determination. The insoluble portion is analyzed todetermine the percentage of pentads (mmmm) according to the methoddescribed above.

EXAMPLES 1-4 AND COMPARATIVE EXAMPLES 1-3

Preparation of Solid Catalyst Components.

Into a 500 ml four-necked round flask, purged with nitrogen, 250 ml ofTiCl were introduced at 0° C. While stirring, 10.0 g of microspheroidalMgCl₂*2.8C₂H₅OH(prepared according to the method described in ex.2 ofU.S. Pat. No. 4,399,054 but operating at 3,000 rpm instead of 10,000)were introduced. As internal donor(s), 7.6 mMols of a previouslyprepared mixture of esters were also added. Type(s) of internal donorsand amounts are reported in Table 2.

The temperature was raised to 100° C. and maintained for 120 min. Then,the Stiring was discontinued, the solid product was allowed to settleand the supematant liquid was siphoned off.

250 ml of fresh TiCl₄ were added. The mixture was reacted at 120° C. for60 min and, then, the supernatant liquid was siphoned off. The solid waswashed six times with anhydrous hexane (6×100 ml) at 60° C. Finally, thesolid was dried under vacuum and analyzed. The types and amounts ofesters (wt %/o) and the amount of Ti (wt %Yo) contained in the solidcatalyst component are reported in Table 2.

Polymerization Examples 5-17 and Comparative Examzples C4-C10

In a 4 liter autoclave, purged with nitrogen flow at 70 ° C for one our,75 ml of anhydrous hexane containing 7 mMols of AlEt₃, the externaldonor ( type and amount are reported in the Table 3) and 10 mg of solidcatalyst component were introduced in propylene flow at 30° C. Theautoclave was closed, 1.5 Ni of hyrogen were added and then, understirring, 1.2 Kg of liquid propylene were fed. The temperature was risedto 70° C. in five minutes and the polymerization was carried out at thistemperature for two hours. The unreacted propylene was vented, thepolymer was recovered and dried at 70 ° C. under vacuum for three hoursand, then, weighed and fiactionated with o-xylene to determine theamount of the xylene insoluble (X.I.) fraction at 25° C. and itsmicrostructure.

Polymerization results are reported in Table 3. TABLE 1 ED/Mg ratio AED/Mg ratio A ED ED (mMols/gram (mMols/gram extracted Type atom) atom)(mol %) rac Diethyl 2,3- 65.2 62.8 4 diisopropylsuccinate Meso Diethyl2,3- 39.3 23.9 39 diisopropylsuccinate Diisobutyl phthalate 48.8 8.8 82

TABLE 2 Preparation conditions Composition Fed in the preparation % ofnot Not not extractable extractable extractable Extractable succinateEx. succinate Extractable ED Ti succinate ED on total I.D. N^(o) TypeMMols Type(s) Mmols Wt % Type Wt % Type Wt % Mols %. 1 A 0.76 B 6.84 3.3A 2.4 B 7.6 24 2 A 1.14 B 6.46 3.8 A 3.24 B 7.56 30 3 A 1.67 B 1.37 4.2A 3.53 B 1.17 30 DIBP 4.56 DIBP 7.6 4 C 1.25 D 1.79 3.4 C 4.4 D 1.46 33DIBP 4.56 DIBP 6.6 C1 — — B 7.6 3.8 — B 10.7 — C2 A 2.8  B 4.8 3.5 A7.75 B 7.45 51 C3 — — DIBP 7.6 2.5 — DIBP 7.1 —A = rac Diethyl 2,3-diisopropylsuccinateB = meso Diethyl 2,3-diisopropylsuccinateC = rac Diisobutyl 2,3-diisopropylsuccinateD = meso Diisobutyl 2,3-diisopropylsuccinateDIBP = Diisobutylphthalate

TABLE 3 Polym. Catalyst Ext. Ext. Donor Example Ex. Donor AmountActivity Pentads TREF N^(o) N^(o) Type Mmols Kg/g X.I. % P.I (mmmm) % %wt 25-99° C. % wt 110-114° C.  5 1 G 0.35 33 94.3 5.8 93.2  6 2 G 0.3543 95.8 5.9 94.8 20.1 34.1  7 3 G 0.35 45 97.2 5.3 95    8 3 G 0.18 4896.1 5.2 94.5 20.3 40.9  9 3 H 0.35 47 94.4 5.3 94.1 27.2 28.4 10 3 I0.35 29 97 5.4 96.3 11 3 I 0.18 36 94.5 5.6 95.2 12 3 J 0.35 21 97.1 5.596.1 19.3 52.5 13 3 J 0.18 26 96.1 5.8 96.2 14 3 K 0.35 25 96 5.5 96.515 3 K 0.18 31 95.4 6.1 96.3 21.4 47.6 16 3 L 0.35 50 97.8 5 97.3 17 4 G0.35 66 96.9 5.1 95.2 C4 C1 G 0.35 41 92.5 4.3 — C5 C2 G 0.35 65 96.86.1 96.3 C6 C3 G 0.35 39 94.2 3.5 94.2 C7 C3 H 0.35 34 94.0 4.1 C8 C3 I0.35 15 95.9 3.9 93.8 C9 C3 J 0.35 19 90.8 4.2 93.1 C10 C3 K 0.35 2895.7 4.3 95.9G = TrifluoropropylmethyldimethoxysilaneH = OctylmethyldimethoxysilaneI = Methyl trimethoxysilaneJ = TetramethoxysilaneK = TetraethoxysilaneL = Cyclohexylmethyl dimethoxysilane

1-20. (canceled)
 21. a propylene polymer has ing the followingcharacteristics comprising: (i) a stereoblock content of at least 18% orhigher measured by a TREF method; (ii) a Polydispersity Index of atleast 5; and (iii) a percentage of pentads (mmmm), measured by NMR, nogreater than
 97. 22. The propylene polymer according to claim 21 havinga stereoblock content higher than 20%.
 23. The propylene polymeraccording to claim 21 having a polydispersity index higher than 5.3. 24.The propylene polymer according to claim 21 having a percentage ofpentads lower than 96.5.
 25. The propylene polymer according to claim 21comprising in the TREF analysis, a fraction eluted at a temperatureranging from 110° and 114° C. which accounts for more than 25% of thetotal weight of the polymer.